Penetrative convection in nocturnal atmospheric boundary layer and radiation fog

TL;DR

This paper presents a computational study of penetrative convection caused by radiative cooling in the nocturnal atmospheric boundary layer, explaining fog formation and temperature profiles during clear, calm nights.

Contribution

It introduces a detailed model of penetrative convection in the nocturnal boundary layer, linking radiative cooling effects to fog formation and temperature stratification.

Findings

Stable inversion layer extends hundreds of meters above ground.

Near-surface air can be 2-6°C cooler than the ground.

Convective mixed layer capped by a stable inversion is key to fog development.

Abstract

After the sunset, under calm and clear sky conditions, aerosol laden surface air-layer, cools radiatively to the upper atmosphere. Predominant effect of the radiative cooling on the vertical temperature profile extends to several hundred meters from the surface. This results in the development of a stable, nocturnal inversion layer. However, ground surface, owing to its higher thermal inertia, lags in the cooling process. Due to this about a meter thick air layer just above the ground can be (2-6)deg Celsius cooler than the ground. Thus, at the surface an unstable convective layer is present, which is capped by a stable inversion layer that extends up to several hundred meters. This configuration involving a convective mixed layer topped by a stably stratified inversion layer is a classic case of penetrative convection. Micrometeorological phenomenon at the surface, such as occurrence of fog, is determined by temperature profile, heat and moisture transport from the ground. Here, we present a computational study of the model penetrative convection, formed due to radiative cooling, in the nocturnal atmospheric boundary layer.